Deformation mechanisms and microstructural characteristics of AZ61 magnesium alloys processed by a continuous expansion extrusion approach

The unique continuous extrusion-based severe plastic deformation approaches were proposed recently to process high-performance magnesium(Mg)alloys,while the in-depth deformation mechanisms under such complicated thermomechanical conditions were not well understood.In the present work,the fundamental deformation behaviors of AZ61 Mg alloy from 25 to 400°C were firstly examined under uniaxial compression deformation.Then the deformation mechanisms and microstructural characteristics of AZ61 Mg alloy during continuous expansion extrusion forming(CEEF)were systematically investigated by microstructural observations,finite element and cellular automata simulations.The results showed that the continuous evolutions of temperature,larger strain level and complex stress state with strain rate range of 0∼5.98 s−1 during CEEF brought the distinctive dynamic recrystallization behaviors and texture development in AZ61 Mg alloy,which were different to that of uniaxial compression deformation.In details,a remarkable grain refinement was achieved via CEEF processing due to the simultaneous actions of continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX).Gradually enhanced CDRX were observed from center to edge region,which had significant effects on the texture distribution and texture strength.The c-axis of most grains rotated under distinctive shear strain following parabolic metal flow,resulting in stable fiber texture.In addition,the evolution of the internal texture of the alloy led to an obvious increase in the Schmid factor for the activation of basalc+aslip system.©2022 Chongqing University.Publishing services provided by Elsevier B.V.on behalf of KeAi Communications Co.Ltd.

Force analysis and experimental study of pure aluminum and Al-5%Ti-1%B alloy continuous expansion extrusion forming process

The deformation zone of CONFORM extrusion was divided into primary gripping zone,gripping zone,conical expansion chamber zone,cylindrical zone and sizing zone of die,and corresponding force equilibrium equations were established using the Slab method.The deformation force formulae of CONFORM machine at any wrapping angle with an expansion chamber were obtained.Experiment on pure aluminum and Al-5%Ti-1%B alloy was conducted on the CONFORM machine self-designed.The resistance to deformation of Al-5%Ti-1%B alloy at the deformation temperature of 400℃ and the strain rate of 3.07 s-1 was measured to be 50 MPa using Gleeble-1500 thermal simulation machine.The calculation results of deformation forces for CONFORM process with an expansion chamber for pure aluminum and Al-5%Ti-1%B alloy were given.The experimental CONFORM radial force is in agreement with the radial force obtained by theoretical formula.

Continuous extrusion and rolling forming velocity of copper strip

A new copper strip production technology combined with continuous extrusion and rolling technology was proposed. The roll velocity must first be matched with the continuous extrusion velocity to achieve continuous extrusion and roll forming. The bite condition of continuous extrusion was determined, and the compatibility equation between the roll velocity and parameters such as the extrusion wheel velocity, reduction, and strip size was established through mechanical by plastic theoretical calculations. The finite element model of continuous extrusion and rolling was then established by using the TLJ400 continuous extrusion machine with a roll diameter of 200 mm. The relationship between the continuous extrusion and rolling velocities was determined through numerical simulations by software DEFORM-3D, and the accuracy of compatibility equation of velocity was verified.

Effect of process parameters on sheath forming of continuous extrusion sheathing of aluminum

The effect of flow passage length in the die cavity and extrusion wheel velocity on the shape of aluminum sheath during the continuous extrusion sheathing process was analyzed by using finite element methods based on software DEFORM 3D and experimentally validated. The results show that by increasing the flow passage length, the velocity of metal at the cross-section of sheath tends toward uniformity, the values of the bending angles of sheath gradually approach the ideal value of zero and the cross-section exhibits a better shape. The extrusion wheel velocity has negligible effects on the bending shape and cross-section of the sheath product when a long flow passage is used.

Microstructure evolution of Al-Sr master alloy during continuous extrusion

The microstructure evolution of Al–Sr master alloy during continuous extrusion was investigated using X-ray diffractometer, scanning electron microscope and transmission electron microscope. Results indicate that the continuous extrusion process could change the Al4Sr particles of the alloy significantly in size and morphology. The as-cast needle-like Al4Sr particles are broken into small blocks in upsetting zone and crushed heavily in adhesion zone. Plenty of dislocations get tangled up in right-angle bending zone. Al4Sr particles grow in the extending zone. Finally, Al4Sr particles in products are approximately 28 μm in length. Al2Sr particles precipitate during the process. Compared with products by horizontal extrusion, Al4Sr particles by continuous extrusion are finer and distribute more evenly.

Microstructure and properties of Al-0.70Fe-0.24Cu alloy conductor prepared by horizontal continuous casting and subsequent continuous extrusion forming

A novel process for manufacturing A1-0.70Fe-0.24Cu alloy conductor was proposed, which includes horizontal continuous casting and subsequent continuous extrusion forming （Conform）. The mechanical properties, electrical conductivity and the compressed creep behaviour of the alloy were studied. The results indicate that the Conform process induces obvious grain refinement, strain-induced precipitation of AI7CuzFe phase and the transformation of crystal orientation distribution. The processed alloy has good comprehensive mechanical properties and electrical conductivity. Moreover, a better creep resistance under the conditions of 90 ~C and 76 MPa is shown compared with pure A1 and annealed copper, and the relationship between primary creep strain and time may comply with the logarithmic law. The enhanced properties are attributed to the grain refinement as well as the fine and homogeneously distributed thermally stable A1Fe and A17Cu2Fe precipitation phases.

Dynamical Solidification Behaviors and Metal Flow during Continuous Semisolid Extrusion Process of AZ31 Alloy

In this paper, a novel near-net-shape forming process, continuous semisolid extrusion process （CSEP） of AZ31 alloy was proposed, and the dynamical solidification behaviors and metal flow during the process were firstly investigated. During casting AZ31 alloy by this process, non-uniform microstructure distributions and non- equilibrium solidification region near the roll surface were found in the roll-shoe gap. Microstructural evolution from dendrite to rosette and spherical grains was observed during the casting by CSEP. Casting temperature, roll-shoe gap width and cooling ability have great effect on casting process and metal flow, so these factors should be carefully controlled, a proper casting temperature of 710-750℃ is suggested. The white α phases were strongly stretched during the processing, and the remnant liquids are correspondingly distributes along the solid phase boundaries and also show stripped lines.

Effects of conform continuous extrusion and heat treatment on the microstructure and mechanical properties of Al–13Si–7.5Cu–1Mg alloy

The effects of conform continuous extrusion and subsequent heat treatment on the mechanical and wear-resistance properties of high-alloying Al–13Si–7.5Cu–1Mg alloy were investigated.The microstructures of alloys before and after conform processing and aging were compared by transmission electron microscopy and scanning electron microscopy,respectively.The results reveal that the primary phases were broken and refined by intense shear deformation during conform processing.After the conform-prepared Al–13Si–7.5Cu–1Mg alloy was subjected to solid-solution treatment at 494℃for 1.5 h and aging at 180℃for 4 h,its hardness improved from HBS 115.8 to HBS 152.5 and its ultimate tensile strength increased from 112.6 to 486.8 MPa.Its wear resistance was also enhanced.The factors leading to the enhanced strength,hardness,and wear resistance of the alloy were discussed in detail.

Effects of extrusion speed of continuous extrusion with double billets on welding performance of 6063 Al alloy

During continuous extrusion,the welds were formed at the confluence of two billets.Influences of extrusion wheel rotational speed on micromorphology and properties of welds of 6063 Al alloy were investigated through microstructure observation,tensile test,and SEM analyses.Welding parameters were analyzed using finite element simulation.Results indicated that metal welding was remarkably affected by oxide on outer surface of the double billets during continuous extrusion.Degree of oxide breakage on the welding surface increased due to the evident increase in effective strain rate with increasing extrusion speed.The high temperature induced by increased extrusion speed accelerated the formation of metallurgical bonding.A portion of weld seam lines slowly disappeared,and the proportion of the welding interface that failed to reach metallurgical bonding was also gradually reduced.Tensile strength and elongation of the weld specimen increased with the increase of extrusion speed.

Fabrication of ultra-high strength magnesium alloys over 540 MPa with low alloying concentration by double continuously extrusion

We prepare a new type of patented biodegradable biomedical Mg-Nd-Zn-Zr(JDBM)alloy system and impose double continuously extrusion(DCE)processing.The lowest processing temperature is 250℃for JDBM-2.1Nd and 310℃for JDBM-2.8Nd,which increases with the Nd concentration.The highest yield strength of 541 MPa is achieved in JDBM-2.1 Nd samples when extruded at 250℃and the elongation is about 3.7%.Moreover,the alloy with a lower alloying element content can reach a higher yield strength while that with a higher alloying element content can reach a larger elongation after DCE processing.However,when extruded under the same conditions,the alloy with a higher alloying contents exhibits better tensile properties.

A STUDY OF CONTINUOUS EXTRUSION-CLADDING PROCESSFOR PRODUCTION OF ALUMINUM-CLADDING STEEL WIRE

In this study the process of cladding steel wires with aluminum is investigated experimentally. It is studied how the cladding process and the quality of products are influenced by the aluminum deformation temperature, the wheel speed, the temperature of steel wire, the wire speed and the steel wire tensile force. The relation among the process parameters above is discussed, and the effect of the aluminum deformation temperature on the coating microstructure is analyzed. This paper suggested a reasonable range of process parameters for producing aluminum cladding steel wires.

Defects Formation and Morphology in Large-sized MoSi_2 Rod Prepared by Continuous Extrusion

Incidence of defects in MoSi2 rods prepared by con- tinuous extrusion is dependent on the viscosity of binder. Generally, low viscosity results in surface defects while high viscosity is responsible for inner defects. Cross-section observations indicated that the typical inner defects in sintered MoSi2 rods were large fissure cavity, multiple small holes and single small cavity, of which the characteristic ultrasonic reflection patterns have been experimentally established. Formation of the inner defects is attributed to the inhomogeneous feedstock moving behav- ior in die, which is aggravated with increasing viscosity of binder. Defect free MoSi2 rods were prepared successfully via con. tinuous extrusion by carefully controlling the viscosity of binder.

Fabrication of AZ31 alloy wire by continuous semisolid extrusion process

A novel technology of continuous semisolid extrusion Process(CSEP) was adopted to produce AZ31 alloy structural materials.Effects of technological conditions on the microstructures of AZ31 alloy during CSEP were studied.During the casting process,the non-uniform distribution of microstructures was found in the roll-shoe gap.Microstructure evolution from dendrite to rosette or spherical grains was observed during the casting process by CSEP.The results show that high casting temperature and large cooling intensity can cause non-equilibrium solidification region near the roll surface,large roll-shoe gap width and high cooling intensity can lead to the formation of discontinuous solidification microstructure and slip plane near the shoe surface,which will finally cause the failure of the casting process.The proper casting temperature range of 730-750 °C,the roll cooling intensity of 0.4 L/s and the roll-shoe gap width of less than 10 mm are suggested.Under the suggested conditions,the product with diameter of 10 mm of AZ31 alloy with smooth surface and homogeneous striped microstructure is obtained.The average strength of the product after heat treatment reaches 270 MPa,and the elongation is 16%.

Effect of extrusion wheel angular velocity on continuous extrusion forming process of copper concave bus bar

The continuous extrusion forming process for producing large section copper concave bus bar under different extrusion wheel angular velocities was studied by three-dimensional finite element technology based on software DEFORM-3D. The rigid-viscoplastic constitutive equation was employed in the model. The numerical simulation results show that the deformation body flow velocity in the die orifice increases gradually with the increase of the extrusion wheel angular velocity. But slippage between the rod and extrusion wheel occurs when the extrusion wheel angular velocity is high. The effective stress near the die orifice enhances gradually with increasing extrusion wheel angular velocity. High stress is concentrated in adjacent regions of the flash gap. The effective strain gradient is greater near the abutment than that near the die orifice. The effective strain of the product increases gradually with increasing extrusion wheel angular velocity. In the deformation process, the deformation body temperature increases remarkably due to friction and deformation. So the cooling is necessary in the region of the die and tools.

Study on grain refinement of interstitial-free steel during continuous frictional angular extrusion

To explore the application of severe plastic deformation for grain refinement in steel production, a new method called continuous frictional angular extrusion （CFAE） was applied to refine the grain of interstitial-free steel. The deformation was carried out at room temperature and individual sheet specimens were processed in different number of passes. An overall grain size of 200nm was achieved after 8 passes and the proportion of high-angle boundaries to the total boundaries was more than 60%. Through the characterization of high resolution EBSD, X-ray diffraction （XRD） and hardness testing,this paper discussed the evolution of microstructures and textures during deformation and explored the development direction of the method.

Extrusion force analysis of aluminum pipe fabricated by CASTEX using expansion combination die

To determine the extrusion force of pipe fabricated by continuous casting and extrusion (CASTEX) using an expansion combination die, the metallic expansion combination die was divided into diversion zone, expansion zone, flow dividing zone, welding chamber, and sizing zone, and the corresponding stress formulae in various zones were established using the slab method. The deformation zones of CASTEX groove were divided into liquid and semisolid zone, solid primary gripping zone, and solid gripping zone, and the formulae of pipe extrusion forces were established. Experiments were carried out on the self-designed CASTEX machine to obtain the aluminum pipe and measure its extrusion force using the expansion combination die. The experimental results of radial extrusion force for aluminum pipe are in good agreement with the calculated ones.

Microstructure Evolution of AZ31 Mg Alloy during Change Channel Angular Extrusion

Microstructure evolution of AZ31 Mg alloy during change-channel angular extrusion （CCAE） was investigated. The grains of AZ31 Mg alloy were refined significantly from 500 mm to 15 mm after CCAE deformed at 523 K. Dislocations were induced at the initial stage of extrusion and they rearranged themselves to form dislocation boundaries and sub-grain boundaries during deformation. When the specimen through the horizontal change channel with the strain increased, the sub-boundaries evolved to high angle grain boundaries （HAGB）. The process of grain refinement can be described as continuous dynamic recovery and recrystallization （CDRR）.

425/630 mm超宽铜带坯一次性连续挤压技术及质量控制

研究了425/630 mm超宽紫铜带一次性连续挤压工艺,并对成型过程进行了模拟。结果表明:通过一次性连续挤压成型的425 mm超宽铜排组织均匀细小,抗拉强度平均值大于210 MPa,性能较理想,适合后续进行大变形量压延加工;通过对630 mm超宽铜排一次性连续挤压模型数值模拟,计算得到的理论值与Deform-3D软件模拟结果基本一致。

羰基铁含量对铝铁复合材料电磁屏蔽性能的影响

采用粉末挤压技术制备铝铁复合材料,通过加入磁性吸波材料羰基铁粉来提高材料的磁导率和吸波性,实现对电磁波的有效衰减。研究结果表明,随着铝铁复合材料中羰基铁含量的增加,材料的抗拉强度增大,最高达到166.7 MPa。材料对电磁波的屏蔽效能随羰基铁含量的增加明显增大,其中,Al/10wt%Fe复合材料电磁屏蔽效能最好,磁导率最高,其电磁屏蔽值为120 dB,吸收屏蔽效能占83.3%,磁导率是纯铝的3倍多。

连续挤压铜铬锆合金线材组织和性能研究

通过热压缩实验建立了铜铬锆合金的本构方程,采用有限元模拟软件DEFORM-3D分析了模具尺寸、挤压轮转速对铜铬锆合金连续挤压变形过程的影响,并利用扫描电子显微镜、电子背散射衍射、力学性能实验等分析了连续挤压产品的微观组织、力学性能。结果表明:模具尺寸为5 mm×10 mm时,比尺寸为6 mm×8.4 mm的连续挤压变形温度更高、等效应变更大、挤压轮扭矩更高;挤压轮转速为10 r·min^(-1)时要比转速为7 r·min^(-1)的连续挤压变形温度更高、等效应变更大、挤压轮扭矩更高。连续挤压变形显著细化了铜铬锆合金的晶粒尺寸,当模具尺寸为5 mm×10 mm,而挤压轮转速分别为7和10 r·min^(-1)时,平均晶粒尺寸从2 mm分别细化到0.77和0.54μm;当模具尺寸为6 mm×8.4 mm,而挤压轮转速分别为7和10 r·min^(-1)时,平均晶粒尺寸从2 mm分别细化到0.52和0.40μm。连续挤压变形显著提高了铜铬锆合金的力学性能,模具尺寸为5 mm×10 mm、挤压轮转速为7 r·min^(-1)时产品抗拉强度达到最高的530.75 MPa,比铸态坯料提高了98.3%。